Marker for inflammatory conditions

ABSTRACT

Use of pregnancy-associated plasma protein-A as a marker for inflammatory conditions, and in particular, for acute coronary syndromes is described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/785,893, filed May 24, 2010, now U.S. Pat. No. 7,939,280, which is acontinuation of U.S. application Ser. No. 12/389,983, filed Feb. 20,2009 (now U.S. Pat. No. 7,723,049), which is a continuation of U.S.application Ser. No. 11/516,020, filed Sep. 5, 2006, now abandoned,which is a continuation of U.S. application Ser. No. 11/254,224, filedOct. 18, 2005, now abandoned, which is a continuation of U.S.application Ser. No. 11/062,400 filed Feb. 22, 2005, now abandoned,which is a continuation of U.S. application Ser. No. 10/767,666, filedJan. 29, 2004, now abandoned, which is a divisional of U.S. applicationSer. No. 10/210,339, filed Jul. 31, 2002, now U.S. Pat. No. 6,699,675,which is a divisional of U.S. application Ser. No. 09/760,376, filedJan. 12, 2001, now U.S. Pat. No. 6,500,630.

TECHNICAL FIELD

The invention relates to uses of pregnancy-associated plasma protein-A(PAPP-A) as a marker and therapeutic target for inflammatory conditions,and in particular, for acute coronary syndromes.

BACKGROUND

Pregnancy associated plasma protein-A (PAPP-A) is a high molecularweight glycoprotein originally isolated from human pregnancy serum. Itis routinely used today as an index of placental function and firsttrimester screen for Down's syndrome. No biological function was knownfor PAPP-A until recent evidence linked it to the insulin-like growthfactor (IGF) axis, the dynamic balance between IGF-I, IGF bindingproteins (IGFBP's), and IGFBP proteases that ultimately determines theextent of IGF-dependent cellular events. PAPP-A specifically cleavesIGFBP-4, which releases IGF-I and makes it available to activatereceptors. Lawrence et al. (1999) Proc. Natl. Acad. Sci. USA96:3149-3153; and Durham et al. (1994) J. Bone Min. Res. 9:111-117.

SUMMARY

The invention is based on the use of PAPP-A levels in serum fordiagnosis of inflammatory conditions, and in particular, acute coronarysyndromes (unstable angina, acute myocardial infarction, sudden cardiacdeath, coronary plaque rupture, or thrombosis) in all stages of theiroccurrence. Patients with acute coronary syndromes are at considerablerisk for death and serious complications, and outcomes can be improvedwith appropriate therapy. Thus, rapid and accurate diagnosis of chestpain is critical for patient. Also, there are important implications topredicting which patients are at risk of acute coronary syndromes beforethe syndrome occurs. The results described herein demonstrate that serumPAPP-A levels are elevated in unstable angina and acute myocardialinfarction, are within normal ranges in stable angina, and correlatewith serum levels of high-sensitivity C-reactive protein (CRP) and freeIGF-I. Furthermore, PAPP-A is highly expressed in unstable plaques fromsudden cardiac death patients. Thus, PAPP-A can be used as an earlymarker of inflammatory conditions, and in particular, acute coronarysyndromes.

In one aspect, the invention features a method for diagnosing aninflammatory condition (e.g., an acute coronary syndrome such asunstable angina, sudden cardiac death, or acute myocardial infarction,rheumatoid arthritis, Crohn's disease, or inflammatory bowel disease).The method includes measuring the level of PAPP-A in a biological sample(e.g., whole blood, plasma, or serum) from a non-pregnant patient;comparing the level with that of control subjects; and diagnosing theinflammatory condition based on the level of PAPP-A relative to that ofcontrol subjects. The patient can be diagnosed as having theinflammatory condition if the level of PAPP-A is increased relative tothat of control subjects. The level of PAPP-A can be measured using animmunoassay such as an ELISA. PAPP-A can be captured with anti-PAPP-Apolyclonal antibodies or an anti-PAPP-A monoclonal antibody. The methodfurther can include measuring the level of a polypeptide selected fromthe group consisting of high sensitivity C-reactive protein, creatinekinase MB, troponin I, troponin T, creatine kinase, creatinine,fibrinogen, interleukin-1, and interleukin-6, and diagnosing theinflammatory condition based on the level of the polypeptide and thelevel of PAPP-A relative to that of control subjects.

In another aspect, the invention features an article of manufacture fordiagnosing an inflammatory condition in a non-pregnant patient. Thearticle of manufacture includes an anti-PAPP-A antibody and packagingmaterial, wherein the anti-PAPP-A antibody can be used for measuringPAPP-A levels in a biological sample (e.g., whole blood, plasma, orserum) from the patient, and wherein the packaging material includes alabel or package insert indicating that the anti-PAPP-A antibody can beused for diagnosing the inflammatory condition.

In yet another aspect, the invention features an article of manufacturefor diagnosing an inflammatory condition in a non-pregnant patient thatincludes reagents for measuring levels of a plurality of polypeptides ina biological sample from the patient. The plurality of polypeptidesincludes PAPP-A and one or more of the polypeptides selected from thegroup consisting of high sensitivity C-reactive protein, creatine kinaseMB, troponin I, troponin T, creatine kinase, creatinine, fibrinogen,interleukin-1, and interleukin-6 The biological sample can be selectedfrom the group consisting of whole blood, plasma, and serum.

The invention also features a method for diagnosing an inflammatorycondition that includes administering (e.g., intravenously) to a patientan amount of an antibody having specific binding affinity for PAPP-Aeffective to detectably bind to PAPP-A, wherein the antibody is labeled;detecting the level of the antibody bound to PAPP-A in the patient; anddiagnosing the inflammatory condition based on the level of the antibodybound to PAPP-A. The detecting step can include diagnostic imaging suchas positron emission tomography, gamma-scintigraphy, single photonemission computerized tomography, magnetic resonance imaging,intravascular ultrasound, or functional magnetic resonance imaging. Thelabel can be a radioisotope (e.g., ¹²³I, ¹⁸F, ¹¹¹IN, ⁶⁷Ga, and ⁹⁹ mTc).

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used to practicethe invention, suitable methods and materials are described below. Allpublications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Incase of conflict, the present specification, including definitions, willcontrol. In addition, the materials, methods, and examples areillustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a box plot of circulating PAPP-A levels. The Kruskal-Wallisanalysis for PAPP-A indicated highly significant group differences(p<0.0001).

FIG. 2 is a graph of C-reactive protein levels in the four studiedgroups: non-atherosclerotic controls, stable angina, unstable angina andacute myocardial infarction. The Kruskal-Wallis analysis for C-reactiveprotein indicated highly significant group differences (p=0.0015).

FIGS. 3A and 3B are graphs of the correlation between PAPP-A andC-reactive protein (3A), and between PAPP-A and free IGF-I levels (3B)in patients with acute coronary syndromes (n=37). A significantassociation was found between PAPP-A and C-reactive protein (ρ=0.61,p<0.001), and with free-IGF-I (ρ=0.39, p=0.018).

FIGS. 4A and 4B are graphs of the correlation between PAPP-A levels andthe cardiac necrosis markers troponin I (4A) and CK-MB (4B) in patientswith acute myocardial infarction. No significant association was foundbetween troponin I (ρ=0.33, p=0.18) or CK-MB (ρ=0.23, p=0.36) and PAPP-Alevels.

FIGS. 5A and 5B are graphs of the receiver operating characteristic(ROC) analysis of PAPP-A and C-reactive protein in patients with acutemyocardial infarction (5A) and unstable angina (5B). The area under thecurve (AUC) of PAPP-A was 0.94 in acute myocardial infarction (standarderror=0.03), and 0.88 (standard error=0.05) in unstable angina.Statistically significant differences in AUCs were found between the twomarkers for acute myocardial infarction (p=0.026) and unstable angina(p=0.011). CRP=C-reactive protein.

DETAILED DESCRIPTION

The invention features methods for diagnosing inflammatory conditions ina mammal (e.g., a human patient), including acute and chronicinflammatory conditions, and especially those inflammatory conditions asrelated to vasculature. Non-limiting examples of inflammatory conditionsinclude acute coronary syndromes (unstable angina, acute myocardialinfarction, sudden cardiac death, coronary plaque rupture, orthrombosis), Crohn's disease, inflammatory bowel disease, and rheumatoidarthritis. As described herein, levels of PAPP-A are significantlyhigher in patients with such inflammatory conditions. For example,PAPP-A levels increase 100 fold or more in rheumatoid arthritispatients. PAPP-A levels also are significantly increased in patientswith unstable angina and myocardial infarction. As raised PAPP-A levelsare common in unstable angina and acute myocardial infarction and PAPP-Ais up-regulated in unstable plaques from sudden cardiac death patients,PAPP-A can be used as a marker for such conditions. As described herein,PAPP-A levels above 10 mIU/L identified 17 of 20 unstable anginapatients (85.0%), and 16 of 17 myocardial infarction patients (94.1%).In contrast, diagnostic sensitivities of cardiac-specific troponins andC-reactive protein in unstable angina is low. As described herein,troponin I was elevated in 3 (15%) and C-reactive protein in 10 (50%) ofunstable angina patients. In other studies, only 22% of patients had apositive result for troponin T, 36% had a positive result for troponinI, and 65% had raised C-reactive protein levels. See, Hamm et al., N.Engl. J. Med., 1997, 337:1648-1653 and Liuzzo et al., N. Engl. J. Med.,1994, 331:417-424. Both markers, nonetheless, are associated withunfavorable outcomes when elevated. Thus, PAPP-A seems to be a valuableunstable plaque marker even when troponins and C-reactive protein arenot elevated, potentially identifying high-risk patients who otherwisemight remain undiagnosed. Without being bound by a particular mechanism,PAPP-A may be directly involved in the pathophysiology of acute coronarysyndromes as a metalloprotease, and indirectly through release of IGF-I.

The cDNA sequence of PAPP-A indicates that the serum form is derivedfrom a pre-proprotein with a putative 22-residue signal peptide, apro-part of 58 residues, and a 1547-residue circulating maturepolypeptide. The sequence shows no global similarity to any knownprotein, but it contains two sequence motifs common to the metzincins, asuperfamily of metalloproteases. The sequence also contains threeLin-12/Notch repeats known from the Notch protein superfamily, and fiveshort consensus repeats known from components of the complement system.

Inhibition of PAPP-A activity is useful for treatment of inflammatoryconditions. As described herein, PAPP-A expression is strongest in theinflammatory shoulder of an unstable plaque. Therefore, inhibition ofPAPP-A expression and/or proteolytic function could increase plaquestability. Without being bound by a particular mechanism, PAPP-A as ametalloprotease may be directly involved in plaque vulnerability, evenbefore the plaque becomes clinically manifested. The proform ofeosinophil major basic protein (proMBP), which is disulfide linked toPAPP-A in pregnancy serum to form an approximately 500 kDa 2:2 complex(PAPP-A/proMBP), may be useful for treating inflammatory conditions asproMBP functions as an inhibitor of PAPP-A activity.

In general, methods of the invention include measuring the level ofPAPP-A in a biological sample from a non-pregnant patient and comparingthe level to that from control subjects. An inflammatory condition isdiagnosed based on the level of PAPP-A relative to the control. Thus, itis determined if PAPP-A levels are increased, decreased, or the same asthat of control subjects. If PAPP-A levels are increased relative tothat of control subjects, the diagnosis is that an inflammatorycondition is present. In particular, a PAPP-A threshold value of 10mIU/L can be used to accurately identify patients with acute coronarysyndromes. The level of PAPP-A can be assessed by measuring PAPP-Aprotein, message (mRNA), or activity. Suitable biological samples formeasuring PAPP-A levels include, for example, blood (including wholeblood, plasma, and serum), urine, saliva, oral washings, and tissuebiopsies such as skin, bone, or blood vessel plaque. Blood is aparticularly useful biological sample.

Detection of PAPP-A Protein

PAPP-A protein can be detected, for example, immunologically. Forexample, a sandwich assay can be performed by capturing PAPP-A from abiological sample with an antibody having specific binding affinity forPAPP-A. PAPP-A then can be detected with a labeled antibody havingspecific binding affinity for PAPP-A. Alternatively, standardimmunohistochemical techniques can be used to detect PAPP-A protein,using such antibodies. Antibodies having affinity for PAPP-A/proMBPcomplexes are available. See, for example, Qin et al., Clin. Chem.,1997, 43(12):2323-2332. Monoclonal antibodies having specific bindingaffinity for PAPP-A, but not for PAPP-A/proMBP complexes, can beproduced through standard methods.

In general, PAPP-A not complexed to proMBP can be produced in variousways, including recombinantly, or can be purified from a biologicalsample, and used to immunize animals. To produce recombinant PAPP-A, anucleic acid sequence encoding PAPP-A polypeptide can be ligated into anexpression vector and used to transform a bacterial or eukaryotic hostcell. In general, nucleic acid constructs include a regulatory sequenceoperably linked to a PAPP-A nucleic acid sequence. Regulatory sequencesdo not typically encode a gene product, but instead affect theexpression of the nucleic acid sequence. In bacterial systems, a strainof Escherichia coli such as BL-21 can be used. Suitable E. coli vectorsinclude the pGEX series of vectors that produce fusion proteins withglutathione S-transferase (GST). Transformed E. coli are typically grownexponentially, then stimulated with isopropylthiogalactopyranoside(IPTG) prior to harvesting. In general, such fusion proteins are solubleand can be purified easily from lysed cells by adsorption toglutathione-agarose beads followed by elution in the presence of freeglutathione. The pGEX vectors are designed to include thrombin or factorXa protease cleavage sites so that the cloned target gene product can bereleased from the GST moiety.

Mammalian cell lines that stably express PAPP-A can be produced by usingexpression vectors containing the appropriate control elements and aselectable marker. For example, the eukaryotic expression vectorpcDNA.3.1+ (Invitrogen, San Diego, Calif.) is suitable for expression ofPAPP-A in, for example, COS cells or HEK293 cells. Followingintroduction of the expression vector by electroporation, DEAE dextran,or other suitable method, stable cell lines are selected. In anexpression system using pcDNA3.1+ and HEK293 cells, yield of the proteinwas about 5 μg/ml. The secreted product was a dimer devoid of proMBP.Alternatively, PAPP-A can be transcribed and translated in vitro usingwheat germ extract or rabbit reticulocyte lysate.

In eukaryotic host cells, a number of viral-based expression systems canbe utilized to express PAPP-A. A nucleic acid encoding PAPP-A can becloned into, for example, a baculoviral vector and then used totransfect insect cells. Alternatively, the nucleic acid encoding PAPP-Acan be introduced into a SV40, retroviral or vaccinia based viral vectorand used to infect host cells.

Recombinant PAPP-A (rPAPP-A) is immunoreactive against all availablemonoclonal antibodies in ELISA and in Western blotting. RecombinantPAPP-A is secreted as a homodimer of about 400 kDa and, after reduction,yields monomers of about 200 kDa. rPAPP-A is active and cleaves IGFBP-4in an IGF dependent manner. Recombinant PAPP-A is about 100-fold moreactive than PAPP-A/proMBP complex in pregnancy serum.

PAPP-A can be purified using standard protein purification techniques.For example, PAPP-A can be purified from conditioned media by passingover iminodiacetic acid immobilized to SEPHAROSE®6B (a crosslinked,beaded-form of a polysaccharide polymer material) loaded with Zn². Afterelution of bound proteins with a stepwise decreasing pH gradient, the pH5.0 fraction can be purified further by passing over a wheat germagglutinin column. Bound proteins can be eluted with a Tris-saltsolution, then by N-acetylglucosamine. Alternatively, a heparinSEPHAROSE® column can be used and PAPP-A is eluted with an increase insalt concentration to 1000 mM. Fractions containing PAPP-A, as measuredwith PAPP-A specific antibodies or with a specific protease activityassay, can be pooled, concentrated, then assessed by SDS polyacrylamidegel electrophoresis. In reducing SDS/PAGE, the molecular mass of PAPP-Amonomer is approximately 200 kDa.

Various host animals can be immunized by injection of PAPP-A. Hostanimals include rabbits, chickens, mice, guinea pigs and rats. Variousadjuvants that can be used to increase the immunological response dependon the host species and include Freund's adjuvant (complete andincomplete), mineral gels such as aluminum hydroxide, surface activesubstances such as lysolecithin, pluronic polyols, polyanions, peptides,oil emulsions, keyhole limpet hemocyanin and dinitrophenol. Polyclonalantibodies are heterogenous populations of antibody molecules that arecontained in the sera of the immunized animals. Monoclonal antibodies,which are homogeneous populations of antibodies to a particular antigen,can be prepared using a PAPP-A polypeptide and standard hybridomatechnology. In particular, monoclonal antibodies can be obtained by anytechnique that provides for the production of antibody molecules bycontinuous cell lines in culture such as described by Kohler, G. et al.,Nature, 256:495 (1975), the human B-cell hybridoma technique (Kosbor etal., Immunology Today, 4:72 (1983); Cole et al., Proc. Natl. Acad. Sci.USA, 80:2026 (1983)), and the EBV-hybridoma technique (Cole et al.,“Monoclonal Antibodies and Cancer Therapy”, Alan R. Liss, Inc., pp.77-96 (1983)). Such antibodies can be of any immunoglobulin classincluding IgG, IgM, IgE, IgA, IgD, and any subclass thereof. Thehybridoma producing the monoclonal antibodies of the invention can becultivated in vitro and in vivo.

Antibody fragments that have specific binding affinity for PAPP-Apolypeptide can be generated by known techniques. For example, suchfragments include but are not limited to F(ab′)2 fragments that can beproduced by pepsin digestion of the antibody molecule, and Fab fragmentsthat can be generated by reducing the disulfide bridges of F(ab′)2fragments. Alternatively, Fab expression libraries can be constructed.See, for example, Huse et al., Science, 246:1275 (1989). Once produced,antibodies or fragments thereof are tested for recognition of PAPP-A bystandard immunoassay methods including ELISA techniques,radioimmunoassays and Western blotting. See, Short Protocols inMolecular Biology, Chapter 11, Green Publishing Associates and JohnWiley & Sons, Edited by Ausubel, F. M et al., 1992. Antibodies havingaffinity for PAPP-A are identified in a positive selection. Antibodiesidentified in such a selection can be negatively selected againstPAPP-A/proMBP, to identify antibodies having specific binding affinityfor epitopes of PAPP-A that are not accessible in the specific complexof PAPP-A and proMBP.

Detection of PAPP-A Message

PAPP-A message can be detected, for example, by a polymerase chainreaction (PCR) assay. In general, PCR refers to amplification of atarget nucleic acid, using sequence information from the ends of theregion of interest or beyond to design oligonucleotide primers that areidentical or similar in sequence to opposite strands of the template tobe amplified. PCR can be used to amplify specific sequences from DNA aswell as RNA, including sequences from total genomic DNA or totalcellular RNA. Primers are typically 14 to 40 nucleotides in length, butcan range from 10 nucleotides to hundreds of nucleotides in length. PCRis described, for example in PCR Primer: A Laboratory Manual, Ed. byDieffenbach, C. and Dveksler, G., Cold Spring Harbor Laboratory Press,1995. Nucleic acids also can be amplified by ligase chain reaction,strand displacement amplification, self-sustained sequence replicationor nucleic acid sequence-based amplification. See, for example, Lewis,R., Genetic Engineering News, 12(9):1 (1992); Guatelli et al., Proc.Natl. Acad. Sci. USA, 87:1874-1878 (1990); and Weiss, R., Science,254:1292 (1991).

For example, the levels of PAPP-A mRNA can be detected using reversetranscription-polymerase chain reaction (RT-PCR) assay. See, forexample, WO 00/54806. In particular, PAPP-A cDNA can be coamplified witha deletion variant thereof that is used as an internal standard (IS).The amount of PAPP-A is normalized against the total amount of mRNA inthe sample, determined as the amount of β-actin mRNA. RT-PCR has beenshown to be 1,000-10,000 fold more sensitive than traditional RNAblotting techniques, and can detect and quantitate both PAPP-A andproMBP mRNA in tissue samples.

Products from competitive PCR can be quantified by ion exchangechromatography on an HPLC system, an accurate method that involves aminimum of post-PCR handling. Alternatively, real-time quantitative PCRcan be performed using, for example, the ABI PRISM® 7700 SequenceDetection System and Taqman fluorogenic probes, or the LIGHTCYCLER™Real-Time PCR system from Roche. An internal reference can be used, suchas amplification of the 28S rRNA with limiting primer concentration.This method allows quantitation down to approximately 500 copies of thetarget sequence.

Detection of PAPP-A Activity

PAPP-A activity can be detected by examining IGFBP-4 proteolyticactivity in a biological sample. For example, a detectably labeledsubstrate can be incubated in the presence of the biological sampleunder suitable conditions, and proteolytic products then are detected.The substrate can be, for example, IGFBP-4 or a fragment thereof. Ingeneral, the reaction can be carried out at 37° C. in a buffer such as 2mM CaCl₂/50 mM Tris (pH 7.5), including IGF-II or fragments thereof, orany other protease activator. Typically, the substrate is labeledradioactively with isotopes such as ¹²⁵I or ³²P, or non-radioactivelylabeled with biotin, digoxygenin, or a fluorophore. Proteolysis ofIGFBP-4 is detected, for example, by examining proteolysis products,such as the 18 and 14 kDa reaction products of IGFBP-4. Radioactiveproteins can be separated by reducing 15% SDS/PAGE and visualized byautoradiography. Proteolytic cleavage products also can be detected byimmunoblotting.

PAPP-A activity also can be detected after capturing PAPP-A withpolyclonal or monoclonal antibodies immobilized, for example, in a wellof a microtiter plate. After washing away unbound protein of thebiological sample, the activity of PAPP-A can be measured with a lowmolecular weight synthetic substrate that liberates a colored productthat can be detected spectrophotometrically. IGF-II or other activatorof PAPP-A can be added with the substrate.

Additionally, PAPP-A activity can be detected by incubating the samplein a well that contains immobilized substrate, e.g., IGFBP-4. Substrateis specifically labeled, i.e., radioactively or non-radioactively. Uponproteolytic cleavage of the substrate, labeled fragments are liberatedinto the liquid phase and can be detected. Substrate can be immobilized,for example, by coating with antibodies or IGF-II.

Labeling can also be accomplished by using IGFBP-4 expressed withdifferent tags on the N-terminus or C-terminus of the protein, forexample an N-terminal FLAG tag and a C-terminal c-myc tag. This allowsIGFBP-4 to be immobilized with a monoclonal antibody that binds one ofthese tags. Detection of bound IGFBP-4 can then be accomplished bystandard ELISA methodology using, for example, a peroxidase conjugatedmonoclonal antibody that recognizes the other tag. IGFBP-4 can also beimmobilized and detected using monoclonal antibodies that recognize theN-terminus and the C-terminus, respectively. Proteolytic activity willresult in a decreased signal, dependent on the amount of proteinaseactivity and time of incubation.

Diagnosing Inflammatory Conditions by Visualization of PAPP-A In Vivo

Inflammatory conditions also can be diagnosed by administering an amountof an antibody having specific binding affinity for PAPP-A to a patienteffective for visualizing PAPP-A in vivo. In addition, visualizingPAPP-A would allow sites in the body of abnormal accumulations, such asplaques that are potentially vulnerable, to be identified. Suitableantibodies and methods for making antibodies are described above. Theantibody typically is labeled, and diagnostic imaging is used to detectantibody bound to PAPP-A. Diagnosis of the inflammatory condition isbased on the increase of PAPP-A, as described above. Threshold can beset to any level, so a level over normal can be detected. Thus,diagnosis can be made based on the presence or absence of antibody boundto PAPP-A.

Typical labels that are useful include radioisotopes used for imagingprocedures in humans. Non-limiting examples of labels includeradioisotope such as ¹²³I (iodine), ¹⁸F (fluorine), ^(99m)Tc(technetium), ¹¹¹In (indium), and ⁶⁷Ga (gallium). Antibodies can belabeled through standard techniques. For example, antibodies can beiodinated using chloramine T or1,3,4,6-tetrachloro-3α,6α-diphenylglycouril. Antibodies can be labeledwith ¹⁸F through, for example, N-succinimidyl 4-[¹⁸F]fluorobenzoate.See, Muller-Gartner, H., TIB Tech., 16:122-130 (1998); Saji, H., Crit.Rev. Ther. Drug Carrier Syst., 16(2):209-244 (1999); and Vaidyanathanand Zalutsky, Bioconjug. Chem. 5(4):352-6 (1994) for a review oflabeling of antibodies with such radioisotopes.

The labeled antibodies are formulated with a pharmaceutically acceptablecarrier and administered to the patient. In general, the antibodies areadministered intravenously (i.v.), although other parenteral routes ofadministration, including subcutaneous, intramuscular, intrarterial,intracarotid, and intrathecal also can be used. Formulations forparenteral administration may contain pharmaceutically acceptablecarriers such as sterile water or saline, polyalkylene glycols such aspolyethylene glycol, vegetable oils, hydrogenated naphthalenes, and thelike.

The dosage of labeled antibody to be administered will be determined bythe attending physician taking into account various factors known tomodify the action of drugs. These include health status, body weight,sex, diet, time and route of administration, other medications, and anyother relevant clinical factors.

Imaging techniques that can be used to detect PAPP-A in vivo includepositron emission tomography (PET), gamma-scintigraphy, magneticresonance imaging (MRI), functional magnetic resonance imaging (FMRI),single photon emission computerized tomography (SPECT), andintravascular ultrasound.

Articles of Manufacture For Diagnosing Inflammatory Conditions

Antibodies having specific binding affinity for PAPP-A can be combinedwith packaging material and sold as a kit for diagnosing inflammatoryconditions. Components and methods for producing articles ofmanufactures are well known. The articles of manufacture may combine oneor more anti-PAPP-A antibodies or fragments thereof as described herein.In addition, the articles of manufacture may further include reagentsfor measuring levels of a plurality of polypeptides in a biologicalsample, including, for example, antibodies having specific bindingaffinity to the particular polypeptide, secondary antibodies, indicatormolecules, solid phases (e.g., beads) and/or other useful agents fordiagnosing inflammatory conditions. Instructions describing how thevarious reagents are effective for diagnosing inflammatory conditionsalso may be included in such kits. Polypeptides that may be useful tomeasure in combination with PAPP-A include polypeptide markers ofinflammation, markers correlating with increased risk of unstable anginaor myocardial infarction (e.g., homocysteine), markers of cardiacinjury, and other non-specific markers of inflammation. For example,interleukin-1 (IL-1), IL-6, or neopterin can be assessed in combinationwith PAPP-A as a marker for inflammation. Cardiac markers andnon-specific markers of inflammation include, for example, troponin I orT, hs-CRP, creatine kinase (CK), CK-MB, creatinine, myoglobin, andfibrinogen.

Particular combinations of polypeptides that can be used for diagnosinga patient with acute coronary syndrome include, for example, PAPP-A,troponin I, and CK-MB; PAPP-A, troponin I, and hs-CRP; PAPP-A, CK-MB,and myoglobin; PAPP-A and myoglobin; PAPP-A and hs-CRP; PAPP-A andtroponin I or T; and PAPP-A and CK-MB. In general, myoglobin is notcardiac specific, but is released from infarcted myocardium at an earlystage (about 2-3 hours post infarction) and returns to normal withinabout 24 hours. Cardiac isoforms of troponin I and troponin T arespecific, but appear in the circulation later than myoglobin (5 to 48hours post infarction). Myocardial tissue contains one isoform of CK-MB,while skeletal tissue has different isoforms. Antibodies having specificbinding affinity for such cardiac markers are available commercially.

The anti-PAPP-A antibody can be in a container, such as a plastic,polyethylene, polypropylene, ethylene, or propylene vessel that iseither a capped tube or a bottle. Non-limiting examples of otherreagents that can be included in the kit are, for example, labeled,secondary antibodies that bind to the anti-PAPP-A antibody and buffersfor washing or detecting PAPP-A. Reagents for measuring levels of otherpolypeptides can be included in separate containers or can be includedon a solid phase with anti-PAPP-A antibody, e.g., a handheld device forbedside testing that includes anti-PAPP-A antibody and one or moreantibodies having specific binding affinity for markers of inflammationor in particular, cardiac injury.

The invention will be further described in the following examples, whichdo not limit the scope of the invention described in the claims.

EXAMPLES Example 1 Methods and Materials

Patient population: The study groups consisted of 17 patients with acutemyocardial infarction, 20 with unstable angina, 19 with stable angina,and 13 age-matched control patients without clinical or angiographicevidence of coronary atherosclerosis. Acute myocardial infarction wasdefined as prolonged chest pain accompanied by ST-T segment elevation ordepression evolving into pathologic Q-wave or T-wave inversion confirmedby an elevation of CK-MB fraction of more than twice the upper limit ofnormal, and troponin I>0.5 ng/mL. Unstable angina was defined as restchest discomfort with either ST-T segment depression (greater than orequal to 0.1 mV) or T-wave inversion in 2 or more contiguouselectrocardiographic leads, CK-MB fraction within normal limit, andangiographically proven coronary artery disease. Chronic stable effortangina was diagnosed as chest pain of at least six months duration,evidence of severe coronary artery disease at coronary angiography, andno clinically evident ischemic episodes during the previous week.Exclusion criteria were advanced kidney or liver failure, overt heartfailure, and major surgery or trauma within the previous month. Patientswith known or suspected systemic thrombotic disorders (other than fromcoronary origin), inflammatory diseases, or pregnancy were alsoexcluded. Angiographic severe coronary artery disease was defined as oneor more stenosis with a diameter reduction ≧70% in any major coronaryartery. To identify a possible association between PAPP-A levels and theextent and severity of coronary artery disease discovered atangiography, the Jenkins score was obtained from every patient. Jenkinset al., Br. Med. J., 1978, 2:388-391. Blood samples were taken atcoronary angiography, placed on ice and centrifuged within 30 minutes at1600G for 5 minutes. All samples were analyzed without knowledge of theclinical data. The mean time from the last ischemic episode to bloodsampling was 8.4±3 hours in myocardial infarction and 9.4±3.9 hours inunstable angina.

The study was approved by the Institutional Review Board of the MayoClinic and Foundation, and all patients gave informed consent.

Human Tissue and Analysis: Atherosclerotic arteries were collected atautopsy from 8 patients within 24 hours of sudden death. Sudden cardiacdeath was defined as described by Burke et al., N. Engl. J. Med., 1997,336:1276-1282. Acute plaque rupture, plaque erosion, and stable plaquecharacteristics were also defined as described by Burke et al., supra.

Immunohistochemical staining was performed on 5-mm-thick paraffinsections using a peroxidase-labeled streptavidin-biotin method. Slideswere deparaffinized and rehydrated through the following solutions:xylene twice for 5 minutes, 100% ethanol twice for 1 minute and 95%ethanol twice for 1 minute. Endogenous peroxidase activity was blockedten minutes room temperature (RT) in 1.5% H₂O₂/50% methanol and rinsedin running tap water. Non-specific protein binding sites were blocked byapplying 5% normal goat serum diluted in PBS/0.05% TWEEN20® (polysorbate20) (pH=7.2-7.4) to slides for ten minutes RT. The serum was blotted offand the primary antibody at indicated dilutions was applied andincubated one-hour RT in a humidity chamber. The primary antibody wasrinsed in tap H₂O and blotted, then biotinylated goat anti mouse IgG,diluted 1/400, was incubated on the slides for 30 minutes RT. Slideswere rinsed in running tap H2O, blotted, and streptavidin-horseradishperoxidase diluted 1/500 in PBS/0.05% TWEEN20®+1% normal goat serum wasapplied and incubated 30 minutes RT. The slides were developed with3-amino-9-ethylcarbazole (AEC) and counterstained with hematoxylin.Monoclonal human PAPP-A antibody (234-5) was used at a concentration of20mg/mL (Qin et al., Clin. Chem. 1997, 43:2323-32). Sections were alsostained with antibodies to a-smooth muscle actin (clone 1A4, Dako; 1/50)or antibodies to macrophage CD68 (clone KP-1, Dako; 1/200). Negativecontrols were stained by omitting the primary antibody. Total plaquearea and the percentage of plaque area that stained for PAPP-A wereevaluated. Quantitative analysis of immunohistochemistry was performedusing a quantitative color image analysis system (DiagnosticInstruments, Inc., Sterling Heights, Mich.).

Laboratory Assays: PAPP-A was measured by a sandwich biotin-tyramideamplified ELISA (sensitivity 0.03mIU/L; units from WHO IRP 78/610) usingPAPP-A polyclonal antibodies for capturing and a combination of PAPP-Amonoclonal antibodies for detection. See, Oxvig et al. (1994) Biochim.Biophys. Acta 1201:415-423 and Qin et al. (1997) Clin. Chem.43:2323-2332 for a description of the polyclonal and monoclonalantibodies, respectively.

The quantitative determination of CRP was achieved by latex particleenhanced immunoturbidimetric assay (Kamiya Biomedical Corp., Seattle,Wash.). Latex particles coated with antihuman CRP antibodies aggregatein the presence of serum CRP forming immune complexes. The formedimmune-complexes cause increased turbidity (measured at 572 nm) that isproportional to the concentration of CRP in the serum.

Total IGF-I was measured by a commercially available assay (DSL-5600Active IGF-I, Diagnostic Systems Laboratories Inc., Webster, Tex.).Assay of plasma IGF-I is complicated by the presence of IGF-bindingproteins, which may sequester IGF-I in the reaction mixture. Daughadayand Rotwein (1989) Endocrin. Rev. 10:68-91. The procedure employs atwo-site immunoradiometric assay (IRMA) including a simple extractionstep in which IGF-I is separated from its binding protein in serum.Powell et al. (1986) J. Clin. Endocrinol. Metab. 63:1186-1192. FreeIGF-I was assayed by a commercially available coated-tube IRMA kit(DSL-9400 Active free IGF-I, DSL Inc., Webster, Tex.). The free IGF-IIRMA is a non-competitive assay used to measure the dissociable fractionof IGF-I. Frystyk et al. (1994) 348:185-191.

CK-MB isoenzyme and cardiac troponin I (cTnI) were measured with animmunochemiluminometric assay (Chiron Corp, Emeryville, Ca).

Statistical Analysis Histologic data are presented as mean±SD. Erodedand ruptured plaques were compared to stable plaques by means ofstudent's t test. Differences in demographic and angiographiccharacteristics between groups were compared using analysis of varianceor two-way cross-tabulation with χ² when appropriate. Data on PAPP-A,free-IGF-I, total IGF-I, and C-reactive protein, which were notdistributed normally, were summarized by medians and box plots, andcompared among groups by the Kruskal-Wallis test. When this showedsignificant group differences, pairwise group comparisons were madeusing the Wilcoxon rank sum statistic. Associations among circulatinglevels of these proteins were assessed by Spearman's rank correlationcoefficient. Associations of PAPP-A with patient risk factors, and groupcomparisons of PAPP-A adjusted for these risk factors, were assessedusing multiple linear regression with logarithm of PAPP-A as thedependent variable. Receiver operating characteristic (ROC) analysis wasperformed on PAPP-A and C-reactive protein for myocardial infarction andunstable angina. The areas under the curve were compared between PAPP-Aand C-reactive protein by the method of DeLong et al. (Biometrics, 1988,44:837-845). P values less than 0.05 were considered statisticallysignificant.

Example 2 Tissue PAPP-A Expression in Unstable Plaques

Four ruptured plaques and four plaque erosions were identified as theculprit unstable plaques in the autopsy series. Four stable plaques werealso characterized. No statistically significant differences in plaqueburden were identified between ruptured (7.1±1.4 mm²), eroded (8.0±3.7mm²), and stable plaques (5.7±2.1 mm²). In plaques with large lipidcores and cap rupture, PAPP-A stained mostly in the inflammatoryshoulder region, in areas surrounding the lipid core, and co-localizedwith CD68-positive cells. In fibrous plaques with superficial erosion,PAPP-A was identified within spindle-shaped smooth muscle cells, in theextracellular matrix, and in non-eroded endothelial cells. Byquantitative image analysis, PAPP-A expression in fibrous eroded plaques(28.3±16.8%) exceeded that in ruptured plaques (18.5±8%), withoutreaching statistical significance (p=0.34). PAPP-A was only minimallyexpressed in stable plaques. By quantitative analysis, PAPP-A expressionin stable plaques (3.2±1.9%) was significantly lower than ruptured(p=0.01) and eroded plaques (p=0.02).

Example 3 Circulating Marker Proteins in Acute Coronary Patients

To determine whether abundant PAPP-A tissue expression in unstableplaques would translate to elevated circulating levels, PAPP-A levelswere measured in patients with acute coronary syndromes (myocardialinfarction and unstable angina) and in stable patients (stable anginaand non-atherosclerotic controls). Table 1 shows age, sex, risk factorprofile, baseline therapy, and angiographic results of the four studiedgroups. Patients with stable angina had three vessel disease more oftenthan myocardial infarction patients (p=0.004), but no statisticaldifferences were observed among the three diseased groups (stableangina, unstable angina, and myocardial infarction) regarding coronaryatherosclerotic burden evaluated by the angiographic Jenkins score(p=0.88). Normal controls tended to have lower levels of the variousrisk factors than the three disease groups, but the three groups werecomparable amongst themselves.

Group data on PAPP-A levels are shown as box plots in FIG. 1. TheKruskal-Wallis test indicated highly significant group differences(p<0.0001). Median serum PAPP-A levels in control patients were 7.4mIU/L (range 3.8 to 11.3 mIU/L), and not significantly different fromthose observed in stable angina (median 8.3 mIU/L; range 4.4 to 22.5mIU/L) (p=0.068). In unstable angina, median PAPP-A levels were 15.0IU/L (range 4.4 to 22.5 mIU/L), significantly higher than those observedfor control (p<0.0001) and stable angina patients (p=0.0002). In acutemyocardial infarction, PAPP-A levels were 20.6mIU/L (range 9.2 to 46.6mIU/L), significantly higher than those observed for control (p<0.0001)and stable angina patients (p<0.0001). Distribution of PAPP-A was notsignificantly different between unstable angina and myocardialinfarction patients (p=0.75). In this study, troponin I and CK-MB levelswere not associated with PAPP-A in patients with acute coronarysyndromes, indicating that PAPP-A response is not induced by myocardialnecrosis.

Using multiple regression models, PAPP-A levels were not associated withage, sex, risk factors or medications. Among the three disease groups,PAPP-A levels were significantly inversely associated withatherosclerosis evaluated as number of vessels with significant lumenstenosis (1- to 3-vessel disease) (p=0.037), but were not associatedwith the Jenkins score (p=0.27). This reflects the coexistence in thecoronary tree of quiescent atherosclerotic plaques with active,vulnerable or fissured plaques.

TABLE 1 Demographic and angiographic characteristics of control patientsand patients with stable angina, unstable angina, and acute myocardialinfarction Stable Unstable Myocardial Control Angina Angina Infarction(n = 13) (n = 19) (n = 20) (n = 17) Age, y (mean ± SD) 58.5 ± 13.2 66.4± 10.9 67.7 ± 11.7 63.4 ± 10.4 Sex, M/F 5/8 15/4 13/7 10/7 Risk factors,n (%) Hypertension 4 (30.8) 9 (47.4) 6 (30) 8 (47) Smokers 0 (0) 4 (21)6 (30) 5 (29.4) Hypercholesterolemia 2 (15.4)* 12 (63.1) 13 (65) 11(64.7) Diabetes 0 (0) 6 (31.6) 6 (30) 2 (11.8) Therapy, n (%) Aspirin 3(23.1)* 17 (89.5) 18 (90) 16 (94.1) β-blocker 3 (23.1)* 15 (79) 13 (65)13 (76.5) ACE Inhibitors 1 (7.7)* 2 (10.5)** 10 (50) 7 (41.2) Nitrates 1(7.7) 2 (10.5) 4 (20) 1 (5.9) Statins 2 (15.4)* 13 (68.4) 13 (65) 11(64.7) Calcium channel 2 (15.4)* 8 (42.1) 6 (30) 0 (0)** blockersAngiography, n (%) 1-vessel disease 0 (0)* 4 (21.1) 6 (30) 7 (41.2)2-vessel disease 0 (0)* 4 (21.1) 7 (35) 8 (47.1) 3-vessel disease 0 (0)*11 (57.9) 7 (35) 2 (11.8)** Jenkins Score, mean ± SD 0* 13.3 ± 6.8 13.2± 9.9  12.1 ± 4.9  CRP levels were measured to assess the relation ofPAPP-A to *Significant vs. the three atherosclerotic groups (p < 0.05);**Significant vs. other atherosclerotic groups (p < 0.05) inflammation.

The Kruskal-Wallis analysis for CRP indicated highly significant groupdifferences (p=0.0015). CRP levels were significantly elevated inmyocardial infarction compared to unstable and stable angina patients(p=0.018 and p=0.001, respectively) (FIG. 2), and were slightly butsignificantly elevated in unstable compared to stable angina patients(p=0.0445) (Table 2). Control group CRP levels were only significantlylower than myocardial infarction levels (p=0.0057). CRP wassignificantly associated with PAPP-A in patients with acute coronarysyndromes (ρ=0.61, p<0.0001) (FIG. 3A). CRP levels were not associatedwith age, sex, risk factors, medications, or coronary atheroscleroticburden.

The significant correlation between PAPP-A and CRP shows that allpatients with acute coronary syndromes and hs-CRP levels >0.3 ng/mL(levels associated with increased risk of developing myocardialinfarction [see, Haverkate et al., (1997) Lancet, 349:462-466) hadelevated PAPP-A levels >8.9mIU/L. However, 13 patients with acutecoronary syndromes (35.1%) (5 myocardial infarction patients and 8unstable angina patients) showed CRP levels <0.3 ng/mL and high PAPP-Alevels.

TABLE 2 Median (range) for CRP, free-IGF-I and total IGF-I levels incontrol patients and patients with stable angina (SA), unstable angina(UA), and acute myocardial infarction (MI) Control (n = 13) SA (n = 19)UA (n = 20) MI (n = 17) CRP 0.28 (0.08-0.8) 0.16 (0.02-5.2) 0.3(0.03-9.7) 1.03 (0.07-9.9) (mg/dL)* Free-IGF-I 0.9 (0.3-3.9) 0.78(0.4-1.7) 1.2 (0.1-3.5) 1.18 (0.2-5.2) (ng/mL) Total IGF-I 108.8(45.1-374.3) 151.2 (60.2-262.4) 141.3 (21.6-317.2) 112.5 (12.4-251)(ng/mL) *p = 0.0015 among groups

Free-IGF-I was measured to determine the bioactive circulating level ofIGF-I. It was hypothesized that increased PAPP-A levels would yieldincreased free IGF-I levels by IGFBP-4 proteolysis. No statisticaldifferences in free IGF-I levels were found between groups, but a weak,yet significant, correlation was observed with PAPP-A levels (ρ=0.39;p=0.018; FIG. 3B) in patients with acute coronary syndromes. The freefraction of circulating and locally synthesized IGF-I induces vascularsmooth muscle cell migration, and is important for monocyte chemotaxis,activation and cytokine release within the atherosclerotic lesion. Nodifferences were found for total IGF-I levels between unstable andstable patients, and no association with PAPP-A levels was observed(Table 2).

CK-MB levels were not increased in blood samples obtained from unstableangina patients, and only 3 of 20 patients with unstable angina hadtroponin I levels above normal (1.6±0.7 ng/mL). Peak troponin I andCK-MB levels in myocardial infarction patients rose to 60.9 ng/mL(range, 1.3 to 368 ng/mL) and 76.3 ng/mL (range, 4.4 to 341 ng/mL),respectively. In these patients, there were no significant correlationsbetween troponin I (ρ=0.34; p=0.19) or CK-MB (ρ=0.24; p=0.36) and PAPP-Alevels (FIGS. 4A and 4B). Even when unstable angina and myocardialinfarction patients were combined, there was no significant associationbetween troponin I (ρ=0.07, p=0.69) or CK-MB (ρ=0.10, p=0.57) and PAPP-Alevels. Therefore, the elevated PAPP-A levels in these patients cannotbe attributed to myocardial necrosis.

Example 4 PAPP-A as a Diagnostic Marker of Acute Coronary Syndromes

The area under the curve (AUC) of ROC analysis for PAPP-A was 0.94 inmyocardial infarction (standard error=0.03), and 0.88 (standarderror=0.05) in unstable angina, pooling stable angina and controlpatients as the stable group. In a parallel analysis, C-reactive proteinhad an AUC of 0.81 (standard error=0.07) in myocardial infarction, andof 0.67 (standard error=0.08) in unstable angina. These differences inAUCs between the two markers were significant both for myocardialinfarction (p=0.026) and for unstable angina (p=0.011) (FIGS. 5A and 5B,respectively). These data suggest that PAPP-A is a valuable marker,significantly better than C-reactive protein, for the identification ofpatients with acute coronary syndromes.

The discriminant power (combined sensitivity and specificity) for acutecoronary syndromes was best at PAPP-A levels of 10 mIU/L. Thesensitivity and specificity of PAPP-A levels >10 mIU/L to identify acutecoronary syndromes were 89.2% and 81.3%, respectively. For myocardialinfarction, the sensitivity of PAPP-A levels >10 mIU/L was 94.1% and forunstable angina 85.0%, respectively. In non-atherosclerotic controlsonly 1 of 13 patients (7.7%) showed PAPP-A levels >10 mIU/L, and 5 of 19patients (26.3%) with stable angina had PAPP-A levels >10 mIU/L.

Example 5 PAPP-A Levels in Rheumatoid Arthritis Patients

PAPP-A levels were assessed in serum samples from 16 patients withRheumatoid Arthritis. Values ranged from 3 to >2000 mIU/ml. In 13 of 16patients, PAPP-A levels were >119 mIU/ml (119 to >2000). For comparison,normal subjects (n=30) have a PAPP-A level of 4.32±1.54 mIU/ml). Table 3contains the individual values for the 16 rheumatoid arthritis patients.

TABLE 3 PAPP-A Levels in Rheumatoid Arthritis Patients (mIU/ml) 3 759592 253 14 >2000 377 >2000 119 >2000 905 308 188 192 572 16

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

1. A method for identifying unstable plaques in a patient, said methodcomprising: a) administering to a patient a labeled antibody havingspecific binding affinity for pregnancy-associated plasma protein-A(PAPP-A) effective to detectably bind to PAPP-A; b) detecting thelabeled antibody bound to PAPP-A in said patient; and c) identifyingunstable plaques based on the detection of the labeled antibody bound toPAPP-A in said patient.
 2. The method of claim 1, wherein said detectingstep comprises diagnostic imaging.
 3. The method of claim 2 , whereinsaid diagnostic imaging comprises positron emission tomography,gamma-scintigraphy, single photon emission computerized tomography,magnetic resonance imaging, intravascular ultrasound, or functionalmagnetic resonance imaging.
 4. The method of claim 1, wherein said labelis a radioisotope.
 5. The method of claim 4 , wherein said radioisotopeis selected from the group consisting of ¹²³I, ¹⁸F, ¹¹¹In, ⁶⁷Ga, and⁹⁹mTc.
 6. The method of claim 1, wherein the labeled antibody isadministered intravenously.